Study On Influence Of Leakage And Blow-down Condition On Process Parameters Of Supercritical CO₂ Conveying Pipeline

CO₂ capture,utilization and storage（CCUS）technology relates to the capture and storage of CO₂ from industrial emissions and storage to the depths of the ground.China’s CCUS technology is either still in its infancy,lacking relevant technologies in CO₂ pipeline transportation and safe operation.Therefore,based on the extension of the 360,000 tons/year CCUS project in the oilfield,this paper studies the supercritical CO₂ pipeline transportation technology with impurities,and studies the pipeline shutdown,start-up and venting process based on steady-state transportation.Pseudo-critical zone pulsation impact law,leakage dry ice generation time,venting and time and phase change process under shutdown conditions.Firstly,the PR equation is chosen as the equation of state for the calculation of the physical properties of CO₂ containing impurities.The phase and physical properties of the CO₂ containing impurities is studied by HYSYS software.The critical point of CO₂ containing impurities is Tc=30.38℃,Pc=7.55 MPa,compared with pure CO₂,the critical temperature of CO₂ containing impurities decreases,the critical pressure increases,and the two-phase region appears in the phase diagram,indicating that the presence of impurities increases the difficulty of CO₂ pipeline transportation;near the critical point,the temperature Small changes will cause a large change in the density of the CO₂ fluid.Water transport and heat equation of the CO₂ containing impurities are derived.Through the comparison of OLGA software and experiment,the venting conditions were studied.The experimental and simulation results were basically consistent,and the feasibility of the software was verified.The OLGA software was utilized to analyze the sensitivity of different temperatures,pressures and flows during steady-state transportation.The variation of fluid process parameters and the distance between supercritical and dense phase demarcation points was obtained under different working conditions.Under the condition of a pipeline shutdown,the effects of initial condition temperature and flow rate on shutdown are studied.The effects of pulsation impact time and initial conditions on the variation of pulsation impact under different initial conditions are obtained.There was not any pressure surge in the restart of the stop.Under the condition of pipeline leakage,the effects of pressure,temperature and pore size on leakage transients were studied.The variation of process parameters,phase transformation process and dry ice generation time under different initial conditions were obtained.In the case of venting,the effects of initial conditional pressure and temperature on venting were studied,and the variation of process parameters,phase transition process and venting end time under different initial conditions were obtained.Under the shutdown condition,with the increase of the stoppage time,the quasi-critical zone enters the quasi-critical zone under different initial conditions,and the pressure and flow pulsation impact occur,but the pulsation amplitude is small,which is within the safe bearing range of the pipeline,so it is not necessary during the shutdown process.Consider the influence of pulsating shock in the quasi-critical section on the safe shutdown of the pipeline;when stopping and restarting,there is no need to consider the damage caused by the pressure increase.When leaking,the leaking port will produce dry ice,so the pipeline material needs to have low temperature resistance;in order to shorten the venting time,it is recommended to use low pressure for venting.